The
"Old World Warblers," when assigned to the traditional family
Sylviidae, once included ~400 species, the second largest family in the
world. New molecular information has shown that this huge "Old World
Warbler" assemblage actually represented a dozen different major
evolutionary lineages; Alström et al. (2006), Jønsson &
Fjeldså (2006), Barker et al. (2004); for an overview see a
discussion of the Break-Up of the Old World Warblers.
Alström et al. (2006) began the inevitable process of breaking
them up into new families, proposing Family names for several of the
lineages and leaving others for later studies. They proposed the Family
name Cettiidae for a group of diverse 'warblers' from Eurasia, and even
a couple 'tailorbirds' from the Orient. Together, these might now be
called the Cettid Warblers, or, more simply and accurately, Cettids
[pronounced "Chet-ids"].

Perhaps the 'core' group in the Cettiidae are the 16 species of bush-warblers in the genus Cettia. These are notorious skulkers, often heard but seldom seen. An example is Philippine Bush-Warbler
(left), endemic to the mountains of northern Luzon, Philippines. In
this lucky shot, we see they shy bird spreading its wings and
sun-bathing in a sunbeam penetrating the otherwise thick undergrowth.
This species is presumably not photographed often.

In
English parlance this family is often called "Bush-Warblers &
allies," and there are about 16 species whose English name is
"Bush-warbler" in this set. However, there are about a dozen or
"Bush-warblers" in family Locustellidae, most of them in genus Locustella.
So it is probably better to call our group Cettids. The Clements world
checklist (2011 update) attempted to bring better clarity to the
English names of various skulking "warblers." A number of African Bradypterus
warblers were once called "bush-warblers" also, but they are now all
termed "swamp-warblers," "rush-warblers," and other more descriptive
names. Unfortunately, this leaves both Cettid "bush-warblers" and
Locustellid "bush-warblers" in tropical Asia. Both types of
"bush-warblers" are once seemed related on their dull appearance and
secretive behavior (e.g., Cettia and Bradypterus are
discussed back-to-back in a "traditional" sequence, as in Bairlein
2006), but this is simply convergent evolution in unrelated sets of
small birds (e.g., Alström et al. 2011).

The family name is derived from the first described bird in this set, Cetti's Warbler
(right, in a marvelous shot by Graham Catley). This is a breeding bird
of reedy swamps from western Europe (including Britain) and northwest
Africa across to northwest India. Western populations are resident, but
many eastern populations are migratory. It is a skulker, more often
seen than heard. As the molecular evidence accumulates about this
family and we learn of the true relationships, it may be that the genus
Cettia itself will be restricted to this single species (or a few at most; currently in 2012, many species are included in Cettia).

There
are a series of ground-hugging forest species in the Cettiidae,
including the nearly tail-less stubtails (3 species in genus Urosphena) and tesias (5 species in Tesia).
Stubtails, like Bush-warblers and Cetti's Warbler, are generally plain,
brown, and unremarkable in appearance, but Tesia are different. They
can be remarkably colorful, as exemplified by Chestnut-headed Tesia
(left, in a magical shot by Ramki Sreenivasan from India). This is a
tiny little bird creeping around the jungle floor, and a great treat to
encounter.

The Cettiidae is almost entirely a
Eurasian family but there is a forest floor skulker in the heart of
Africa — Neumann's Warbler Hemitesia neumanni of the
Albertine Rift. It is most likely closest to the Oriental stubtails,
although still somewhat distant; Irestedt et al. (2011). Those authors
called it "the sole African member of a Palaeotropic Miocene avifauna."
This might mean, however, that the Cettiidae arose in Africa and then
expanded to Asia, with various African species thereafter becoming
extinct, leaving only Neumann's Warbler as a relict.

Earlier suggestions that this family might include such African species Green Hylia Hylia prasina, or the Eremomelas, were wrong. Hylia is apparently a long-evolved lineage and may warrant Family status [tentatively so here],
while the Eremomelas are cisticolids. There are still some other
African birds that are closely related to cettids (see below).

Another
surprise revealed by genetic research was that the tailorbirds were not
a unified group. Some tailorbirds proved to be closely related to
cisticolas and prinias [family Cisticolidae] but the two Phyllergates tailorbirds in the Orient proved to be cettids. One of these is Mountain Tailorbird
(right), which ranges from southern Asia to the Philippines and
Wallacea. These tailorbirds had previously been assigned to genus Orthotomus
(see Alström et al. 2006). Thus not only are tesias an example of
colorful cettids, but so are these two tailorbirds (the other Phyllergates is Rufous-headed Tailorbird P. heterolaemus
of the Philippines). While there are many places where these
tailorbirds are undergrowth skulkers, they can be found in canopy of
some montane forests.

The
full parameters of the rest of the Cettiidae is starting to come into
focus (Fregin et al. 2012). In addition to those discussed above, it
includes Broad-billed Warbler Tickella hodgsoni, three warblers in the Asian genus Abroscopus [Yellow-bellied Warbler A. superciliaris, Black-faced Warbler A. schisticeps, and Rufous-faced Warbler A. albogularis]; and the Scrub Warbler Scotocerca inquieta of north African and the Middle East (Alström et al. 2011a).

A year later, Fregin et al. (2012) proposed treating the genus Scotocerca
as a separate family, Scotocercidae. This was based primarily on a
"long internode" in the phylogeny of the Cettiidae The authors
published evidence at Scrub Warbler (left, artwork of two races by John
Gale) was sister to the rest of the Cettiidae, but there are hundreds
of instances in the avian tree of life where a single taxa is sister to
a related clade of species. In my view, this is hardly a reason to
raise Scrub Warbler to a monotypical family level. It is a dull,
skulking, wren-like "warbler" of desert scrub, not particularly
distinct from other retiring cettids. Yes, it proved not to be related
to the Cisticolidae, but has evolved a convergent lifestyle. I leave it
among the Cettiidae, possibly as a subfamily.

Fregin et al. (2012) also proposed treating the genus Erythrocercus
— three "flycatchers" from sub Saharan Africa — as a separate family,
Erythrocercidae. These birds are sister to the clade of Cettiidae plus
Scrub Warbler. One reason for separating them is that they have 12
rectrices rather than the 10 which the other Cettiidae (including Scrub
Warbler) have. Further, they are African rather than Asian; they are
apparently rather ancient (although Fregin et al. 2012 did not give us
a time estimate); and they are distinctive and diagnosable. I have
tentatively accepted this proposal and have named this set Bristle-flycatchers. See that web page for more details. If this proposal does not gain wide acceptance, the bristle-flycatchers in genus Erythrocercus will likely become a subfamily of the Cettiidae.